Something funny happened, I originally wrote this article to comment on the fact that you can get an R9 290X crossfire setup for just $620 but then I realized that some Vesuvius GPUs are selling for as low as $679 ($650 after rebate). Considering the fact that the card originally launched at the $1500 price point, that is an absolutely bonkers price cut. You are paying approximately $340 per core, which is pretty reasonable and believe it or not, you can get the same approximate power for an even lower price.
AMD's Dual GPU Setups Offers the Best Value for 4K at Approximately $620-$680 Retail
You can now get an R9 290X for a mere $309 ($279.9 after rebate) from some vendors and if that isn't pure value, I don't know what is. Put two of these in crossfire and you have got yourself a 4K Ready setup at a dirt cheap price (relatively). The lowest priced R9 290X you can find right now on the market (I am taking Newegg.com as an example platform) is PowerColor PC AXR9 290X with a triple air cooler. This is a relatively small vendor so if you want a name you can trust, increase the budget to $660 and you can get two Gigabyte R9 290Xs with Windofroce 3X coolers (or add an extra $20 for the R9 295X2). This is a pretty decent AIB with a pretty decent design. Not to mention that the air cooler on this card is among the best you can get on the market leaving you some very decent headroom for over clocking. The cheapest R9 295X2 I could find was the XFX Core Edition R9 295X2, which is a pretty reliable AIB.
Why pay the extra $50 to get an R9 295X2
Logically speaking, you should only go with the R9 295X2 if you want to overclock the hell out of your card. However, in some cases it might be feasible for you to pay and benefit in the long run. If you are running out of space in your casing or have a tiny Mini-ITX casing, then the R9 295X2 might be the only way you can get a decent dual GPU. Either way, both of these options offer incredible value, with literally only one downside: the Industry is shifting to low level APIs of which DX12 will form the flagship, something these cards won't support at the hardware feature level.